The present invention relates to a method and apparatus for estimating yaw rate in a wheeled vehicle and more particularly to a method and apparatus that is capable of producing an estimate of yaw rate that can be used in a vehicle stability system.
Gyroscopes are commonly used to provide an estimate of a rate of rotation about a particular axis. In wheeled vehicle applications, a gyro can be used to help guide and navigate a wheeled vehicle. In other wheeled vehicle applications, a single-axis gyro is typically used to feed an estimate of yaw rate to a stability control system that is capable of making adjustments to vehicle operation that help increase vehicle stability under a wide variety of operating conditions.
Vehicle stability control systems commonly include a computer that executes an algorithm that monitors vehicle operation. Usually, several sensors and engine operation is monitored. If the algorithm determines that the vehicle is unstable or is in danger of becoming unstable, vehicle operation is adjusted in a manner intended to increase stability. Usually, vehicle operation is adjusted by applying one or more brakes. Engine speed can also be controlled.
Sensors that are typically monitored include one or more wheel speed sensors, a steering angle sensor, a yaw rate sensor, and a lateral acceleration sensor. During vehicle operation, signals from one or more of these sensors are used to determine an acceptable yaw rate threshold given the speed of the vehicle, its lateral acceleration, and its steer angle. If the actual yaw rate provided from the yaw rate sensor exceeds the acceptable yaw rate threshold, vehicle stability control is initiated.
For example, in at least one stability control system, where a condition known as understeer is detected, the front inside brake is selectively applied. Where oversteer is detected, the outside front brake is selectively applied. Where the vehicle is slipping sideways and sideslip is detected, at least one vehicle stability control system selectively applies at least one brake to increase stability. The amount of power assist applied to the power steering system can also be regulated to help prevent instability during sideslip.
The yaw rate sensor typically is a single-axis gyro and the lateral acceleration sensor typically is an accelerometer. One type of gyro that is commonly used in stability control systems is a fiber optic rate gyro. Other types of gyros can also be used.
However, the gyro makes up a significant portion of the cost of these systems. As a result, use of vehicle control stability systems has generally been limited to more expensive luxury cars. Thus, it is desired to find a more economical solution to obtain yaw rate. It is also desired to produce a less costly vehicle stability control system.
The present invention is directed to an apparatus and method of obtaining estimated yaw rate that can be used as an input into a vehicle stability control system or the like for a wheeled land vehicle. The apparatus includes a pair of longitudinally spaced single axis accelerometers with one of the accelerometers being located in front of a center of gravity of a vehicle and the other one of the accelerometers being located behind the center of gravity. The accelerometers lie along a common axis that preferably is aligned with a vehicle centerline. Preferably, the accelerometer axis overlies the vehicle centerline and can be coincident with it.
The accelerometer outputs are processed by a processor to obtain lateral accelerations that are used as inputs along with steer angle from a steering angle sensor to obtain a yaw rate estimate. The yaw rate estimate preferably is then used as an input to a vehicle stability control system, such as a control system that regulates wheel speed and/or engine speed to increase vehicle stability should the estimated yaw rate fall outside of a desired threshold.
In a method of estimating yaw rate, the lateral accelerations and steer angle are inputted into a statistical estimating algorithm that preferably is recursive to obtain an estimate of yaw rate and lateral vehicle velocity. One or both estimates can then be used as inputs into a vehicle stability control system.
Thereafter, a current steering angle along with the prior estimated yaw rate and lateral velocity are processed to provide a correction to the next input from which the next iteration of estimated yaw rate and lateral velocity are determined. The suit is a method of determining an estimated yaw rate that is fast, simple, and which is noise tolerant and relatively immune to vehicle tilt and roll.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating at least one preferred embodiment of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.